Plastics are easy to mold, and can be easily molded into various shapes. Thus, they are put to wide varieties of uses. In particular, bottles in which the inner surfaces of container walls are formed from polyesters typified by polyethylene terephthalate (PET) are used preferably as containers for accommodating various beverages, edible oils, seasoning liquids, etc.
Bottles for accommodating highly viscous liquids, in particular, are required to exhibit high slip properties on the inner surface of the bottle with respect to liquid contents so that the contents can be discharged promptly and can be used up completely without being left within the bottle.
Recently, various proposals have been made for technologies which enhance slip properties with respect to viscous substances by forming a liquid layer on a resinous surface of a base material (for example, Patent Documents 1, 2).
According to such technologies, the slip properties can be enhanced dramatically as compared with the incorporation of an additive, such as a lubricant, into the resin forming the surface of the base material. Currently, therefore, these technologies are attracting attention.
With the above means for modifying the surface characteristics by forming the liquid layer on the resinous surface, however, the problem arises that it is difficult to sustain the modified surface characteristics for a long term. That is, the liquid forming the liquid layer gradually permeates and diffuses into the underlying resin layer. As a result, the modified surface characteristics disappear over time.
Patent Document 3 by the present inventors proposes that a liquid diffusion preventive layer for preventing the permeation/diffusion of the liquid be provided on the underside of the underlying resin layer under the liquid layer on the inner surface of the container in order to preclude the disappearance over time of the surface characteristics attributed to the liquid layer as mentioned above.
Patent Document 4 proposes a packaging material comprising a composition having an additive with HLB of 5.0 or less incorporated in a range of 0.3 to 3 parts by weight into 100 parts by weight of a polyolefin resin.
The packaging material of Patent Document 4 is excellent in releasability from emulsion-based contents such as chocolate cream or custard cream. That is, such emulsion-based contents minimally adhere to the packaging material, thus avoiding, for example, the disadvantage that the contents deposit in a large amount on the inner surface of a lid material.
Researches by the present inventors, however, have shown that a container formed from such a composition is insufficient to enhance slip properties with respect to fluid contents such as ketchup.